When performing outdoor activities, it is common practice to protect the eyes with suitable eye-protecting devices, such as eyeglasses, masks, goggles and the like. These eye-protecting devices can, but need not be, ophthalmic.
Eye-protecting devices are especially an important safety measure when performing outdoor activities such as riding a motorcycle, cycling, running, skiing, sailing, tennis and the like, in order to protect the eyes from sunlight and/or from possible physical impacts.
Sometimes, these eye-protecting devices are worn under a head protecting device, such as a helmet, in activities such as riding a motorcycle, car racing, downhill skiing, climbing, and the like.
In all the abovementioned situations, the eye-protecting devices are often in the form of the so-called “rimless” devices, such as eyeglasses and wrap around eyeglasses, i.e. devices in which the lenses or visors are not surrounded by the frame along their whole periphery, but are attached to a one-piece or multi-piece supporting structure at certain discrete points or outer portions. The “rimless” devices may possess advantageous features by providing a wider view angle and lightness in weight, which are particularly useful when these devices are worn under a helmet.
In a first arrangement of a “rimless” device of this kind, the lens or the visor may be attached to an upper bar of the frame by means of a suitable fixing means, such as screws or rivets. In another rimless arrangement, usually referred to as the “three pieces eyeglass”, the eye-protecting device is substantially frameless and the lenses are fixed directly on a central nosepiece and on two temples.
Traditionally, the eye-protecting devices suitable for performing outdoor activities include an optical element comprising at least one transparent portion made of a substantially rigid plastic material having suitable characteristics of low weight, transparency, impact resistance and scratch resistance. Rigid plastic materials used to produce these transparent portions include diethylenglycol-bis-allyl-carbonate or CR39®, polycarbonate, polymethyl methacrylate, cellulose esters, polyurethanes and transparent polyamides. Among them, diethylenglycol-bis-allyl-carbonate or CR39® and polycarbonate are most commonly used for the manufacture of eye-protecting devices suitable for use while performing outdoor activities.
Known optical elements made of these rigid materials, however, have not proven to be entirely satisfactory while in use during outdoor activities, especially when performing outdoor sports activities. For example, the optical elements made of CR39®, while having sufficient impact resistance for use in fashion sunglasses, prove to be unsatisfactory when used in sports sunglasses as, for example, “rimless” and “wrap-around” eyeglasses, since their impact resistance drastically diminishes when they are drilled to form the holes necessary to accommodate the fixing means used to attach the optical elements to the frame. Such holes, in fact, render the optical elements more fragile and brittle in case of impacts. Sometimes, the optical element may even break upon sufficient impact and hurt the eyes or the face of the wearer.
The optical elements made of polycarbonate, on the other hand, while having per se a very good impact resistance, possess such poor scratch and chemical resistance that they require an antiscratch coating, which lowers the impact resistance and enhances the “stress cracking” phenomenon. This phenomenon is provoked by an overload of permanent internal tension that exceeds the elasticity limit, causing the lenses to craze, haze and lose mechanical strength. In addition, the stress cracking phenomenon is worsened when the optical elements made of polycarbonate are drilled to form the holes necessary to accommodate the fixing means in the “rimless” devices and also when the optical element is in contact with materials, such as solvents and greases, or with frames releasing chemicals, such as plasticizers.
These chemicals, furthermore, have a deleterious effect on the haze phenomenon when they are absorbed by the optical elements made of polycarbonate.
With regard to the other transparent rigid materials, such as polyamides, polymethyl methacrylate and cellulose esters, similar problems can arise, since they all have chemical, physical and mechanical characteristics similar to or worse than those of CR39® and polycarbonate.
Finally, all the rigid optical elements currently available are affected by two drawbacks that have not yet been overcome, namely: i) the discomfort the optical elements may cause to the wearer when the eye-protecting device is worn in close contact with the skin under the eyes, a situation which is more and more common with eye-protecting devices suitable for performing outdoor activities, and ii) the discomfort and the possible damage the optical elements may cause if the optical element injures the face of the wearer caused by impact, or worse, if the optical element breaks.